Bridge codes in North America have incorporated wood as an approved material for bridges. Bridges with steel girders and wood decking usually consist of wood laminated together by nailing in a “W” pattern about 4″ on center. These bridges suffered from two major disadvantages. The first, the decking is used solely for transmitting loads to the steel girders. The wood does not actively participate or contribute in sustaining the longitudinal moment. The second disadvantage is that the nail connections between the wood laminates become loose after a few years of service, leading to deterioration of the riding surface.
Although timber is a widely used structural material, inherent to many products of nature, the strength and elastic modulus values may vary widely. However it is known that the longitudinal modulus of elasticity has its highest value amongst the various moduli of wood and the compression resistance of timber parallel to the grain is approx. 2.0 to 6.0 times greater than that perpendicular to the grain.
Wood decking utilizing wood beams oriented transverse to the bridge frame has commonly been used in the past. The transverse laminated wood decking cannot share a large portion of the longitudinal moments carried by the steel beams because of the low elastic modulus in the radial and tangential direction is generally about 1/20 of the longitudinal modulus of elasticity.
However, reorienting the decking so that the wood laminates are parallel to the steel beams and developing composite action between the wood laminated deck and the steel girders helps to utilize efficiently the dominant rigidity of the wood decking and higher compressive resistance of the wood laminates to the grain. (i.e. beams parallel to steel can share longitudinal moment). As a result of this reorientation, composite action is achieved.
Prior art has described wrapping individual wood beams with layers of fibreglass to increase the strength and stiffness of the laminated wood beam by cube for every 4 mm of laminate but getting the process correct for large bridge decks requires a great deal of time and money.
In the past, the loosening of nail connections was observed in both transverse laminated and longitudinal laminated wood decks and confirmed to be the cause of reduced load capacity of bridges and/or deteriorated riding surfaces. The post tensioning technique was implemented to prevent the problem of loosening nail connections, helping to rehabilitate many existing bridges and increase the functionality of new bridge designs with longer service life and formulating specifications to design post tensioned bridge decks incorporated into US and Canadian bridge codes.
It would be beneficial to provide a bridge deck and structure comprising a wood core with reliable means of connecting the deck panel components, reliable means of securing the deck panel to the bridge frame, and providing composite longitudinal moment supporting action between the bridge frame and the bridge deck.